Electron beam tube



Dec. 20, 1949 Filed June 26, 1948 Fig.2"

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. l S 12 u "WITNESSES: dyzz INVENTORS Ralph OMclntosh 8 GBlYenn E.Sheppurd.

ATTORNE Patented Dec; 20, 1949 UNITED STATES PATENT on-"role amines ELECTRON BEAM Ralph o. Mandarin and Glenn sheppard, Pittsburgh, Pa., 'assigno'rs :to Westinghouse Electric Corporation, -Ea's t :Fittsburgh, 'Pa., a "corporation of Pennsiivan'ia Application June 26, 1948, Serial No. 35. 185 5 Claims. (01. -250=-27.5.)

Our invention relates to an electrical discharge tub and, in particular, relates to such a tube embodying a novel type of cathode structure adapted to maintain constant spacing between the cathode and other electrodes of the tube despite some variations of temperature of the structure.

Certain types of electron discharge tubes embodying an anode, :at *lea'st'one 'coritrol electrode and a. cathode are designed with very small spacing intervening between the cathode and one of the control electrodes. The cathodes of such tubes are designed to operate at high tempera tures, and due to the substantial coefficients of thermal expansion of the materials employed in i the cathode structure, the dimensions of the cathode naturally change as the temperature changes the "course of operation. Where the spadi'ng between the eontrol each-ode and the cathode -is extremel sine-11, as is the case with certain types of electron tube, these changes of dimensions in the cathode structure tend to alter such spacing by amount'sjwhich produce substantial changes in the electrical characteristics of the discharge tube. In some tubesthe temperature of the cathode is -a controlling factor in the power output of the tube. Thus it is im portant that the cathode position remain fixed as the-temperature is varied to control the power output of the tube. the cathode be uniformly *at the same temperatureover its area.

One object of our invention is, accordingly, :to provide a'noveltypelof'cathode structure in which temperature variations :of the cathode "do not result in "alteration "of the spacing between the electron-emissive surface of the cathode and the associated electrodes in the tube, and in which the active cathode area is uniformly heated and rigid in form.

Another object of our invention is to provide a novel type of cathode structure in which the changes in dimension "of various portions -.of the structure :cancel each other as iar as their eifec't on altering the spacing between the electronemissive surface of the eathode and the control electrode is concerned.

Still another object of our invention is to provide an improved structure for mounting :the electrodes "of an electrical "discharge tube of the hot cathode type.

Other objects of our invention will become apparent upon reading the following description, taken in :connection with the drawing, in amen:

It is also portant 3mm;

J'ligure l isa diagrammaticfshowing :of anelec- 65 2 tribal discharge tube having electrodes embodying the pr inciple's o'i our invention;

Fig. 2 *is aside elevation of a cathode emhodying the principles-of our invention;

Fig.8 is an end elevation or the caithode stltlbeureshown inFig. 2; *and Fig. 4 is a diagram useful in explaining the principles =of our invention.

Referring in detail to the drawing, a vacuum-=- tigh't c'ontair'ie'r l encloses "a nfanode 2 an ac"- eel erator electrode 3, a control elec-trod'e 4 and 5a catl'iode 5, the latter being of a novel form according to the principles of our invention. The cathode 5 is supported on a pair of inleads 6, 1 s'ealed through the walls of the container 1 and terminating in a pair or relatively massive end por t'ions 9. Inleads t, l are relatively massive and well-conducting thermally or the massive end portions :8, 9 ca'n be fluid cooled through inleads #6, 1. Supported on the end portions 8 and 9 lay'so'me suitable means, such as screws i ll, 12. is a thin inetal-shee t bridging member l3 having risers it of relatively restricted cross-section, and having a horizontaiportion '11'5 of larger crosssectional area bridging the space between the ris'er s M. The horizontal portion l5 may be bent form *two aprons iii, H, which "constitute a r -i (1 portion. The upper surface of the portion 15, 16, 1 l may be coated, in a way too well known in the electron cathode art to require detailed description, with a coating of "barium oxide and strontium oxide or other suitable electronemissive material which, with the base metal, ite a 'com'posite iayer -18.

when operating, heating current is conducted 'tllrbugh the reads 5, l and end portions 18, 9 to the 'risrs *l4 -and thence through the bridging rnen ber I 3, thereby raising the temperature of the latt'e'r suiiiciently to produce a satis- -i'a"ct'oiy electron emission from the layer l8. Exter ii'al cu'its well known in the electrical disch'asge tirb' art hiay thereafter be connected "between the leads 6, l and the anode 2 accelerator electrode '3 and-"control electrode 4. Totake'only one muster-its of the arenas which a tube of the type here disclosed is useful, reference may be made to an application of David H. Sloan, Se rial No. 583,257, filed March 17, 1945, for a 'Iube, assigrfieeto the a's'si'gnee oi the present "application. The bridging member [3, It, l5 hi the ifathdde inay, of course, be made of any suitable metal or alloy capable of withstanding the desired operating temperature and having the specific resistivity to generate the heat desired for maintaining the temperature of the layer I8. For example, we have found tantalum to be a suitable material for this bridging member, although nickel or tungsten may be desired for certain specific types of cathode.

A moments consideration will show that the heat generated by the flow of the heating current in the bridging member I3 will cause an expansion in the dimensions of the bridging member I3 and will also result in heat flow through the risers I4 to the terminal portions8 and 9. The latter are designed with sufficient mass, surface area and conductive cooling to dissipate the heat flowing into them before it seriously affects the seals at the inleads 6 and "I. As a result, the portion of the bridging member I3 which supports the emissive layer I8 will stand at an elevated temperature, while the lower ends of the risers I4 will be at the much lower temperature approximating that of the terminal portions 8 and 9. The cross-section of the risers I4 is made small in order to minimize the heat flow to the members 8, 9; and may be so proportioned that the heat generated in it so compensates for that flowing to the end portions 8 and 9 as to avoid substantial temperature gradient between the midpoint and the ends of horizontal portion I of the cathode.

As a result of the high temperature to which the horizontal portion l5 of the bridging member I3 is heated, the length of portion I 5 will increase when the tube is put in operation, but at the same time the lesser temperature rise of the risers It will expand their length to a substantially smaller degree. The increase in length of the portion I5 will displace the upper ends of the risers I4 in a horizontal direction so that the angle between them will increase; and except for the above-mentioned concomitant expansion in length of the risers I4 mentioned in the preceding sentence, this displacement would result in displacing the bridging portion I5 downward toward the terminal portions 8 and 9. However, this downward displacement tends to be compensated by the expansion in length of the risers I4 and by properly proportioning the length of IV the latter to the length of the horizontal portion IE, it is possible to make these opposite tendencies toward vertical displacement of the horizontal portion I5 exactly compensate and cancel each other.

The relation between the above-mentioned lengths which will result in such compensation may be determined in the following way.

In Fig. 4, we diagram the hot, flat surface I5 of half -length A supported by risers it from fixed end portions 8 and B which have the half spacing S. The distance B can be measured from the line of support to the end of surface I5. It is possible to measure the minimum angle U be tween the line of B and the surface I5, which, as Fig. 2 shows, is also the angle between the line of B and the surface through the support line and parallel to surface I5.

The condition that the surface I5 remains fixed in distance from end portion 51 is met if where dA is the reversible incremental increase in A (here due to increase in the temperature of surface i5) and dB is the corresponding simultaneous increase in B.

The validity of this condition may be shown as follows:

B sin U is to remain constant Taking the differential,

(2) d(B sin U)=0=dB sin Ul-B cos UdU dB sin U (3) B cos U From the geometry of the structure,

(4) 11:]? cos U+S taking the differential,

(5) dA=dB cos UB sin U (W substituting from (3) in this equation for dU dB sin U cos U-I-sin U dA=dB 00S U+Bm=dB co U dB (7) Therefore cos U We also have another expression for U by the geometry:

(9) Thus, from (7) and (8) temperature causes a small AA and AB which can be measured. The ratio as AA is approximately equal to and thus determines cos U, which in turn determines S.

It is expressly our intent to use structures which have angle U greater than 0 degrees and less than degrees.

While we have equated the displacement d(B sin U) to zero in Equation 2 to represent a zero change in the separation of the cathode from the other electrodes, it will be evident that in certain cases it may be desirable that this separation vary at a predetermined rate with cathode temperature changes and in such cases the said predetermined rate should be substituted for zero in the second member of Equation 2.

Since the net displacement of the cathode in the vertical direction remains zero, its change in distance from the other electrodes 2, 3 and 4 will likewise remain zero, and the desired result of preventing variations in temperature of the cathode 5 from changing its spacing away from the electrode 4 will have been attained.

While we have described our invention as used to maintain a desired separation of the heated cathode of an electrical discharge tube from other electrodes therein, it may be applied in Ways evident to those skilled in the art to maintain a desired separation between other heated surfaces cos U= and structural elements operatively supported adjacent to them; as, for example, in furnaces, ovens, toasters, dryers and the like.

We claim as our invention:

1. A cathode structure for an electrical discharge tube comprising a member of sheet metal having a central portion of length 2A supported by end portions making angles U therewith from two terminal blocks maintained at a relatively low temperature, the distance between the adjacent ends of said terminal blocks and the ends of said central member being equal to B, the values of A, B and U being related approximately in accordance with the following formula:

gg=cos U where dA and dB are respectively the increases in A and B resulting from a small increase in temperature of said central portion.

2. A cathode structure for an electrical discharge tube comprising a member of sheet metal having a central portion of length 2A supported by end portions making angles U therewith from two terminal blocks provided with means for efliciently dissipating heat, the distance between the adjacent ends of said terminal blocks and the ends of said central member being equal to B, the values A, B and U being related approximately in accordance with the following formula:

g=cos U where dA and dB are respectively the increases in A and B resulting from a small increase in temperature of said central portion.

3. An electrical discharge tube comprising a vacuum-tight container having an anode, at least one control electrode and two cathode-support members supported from said container the distance between said cathode-support members and said control electrode being substantially fixed, a cathode of sheet metal supported on said cathode-support members and comprising a first portion and two second portions making an angle U therewith, means attaching said second portions to said cathode-support members so that the distance between the ends of said first portion and the end of said cathode-support members is B, the length of said first portion being 2A, and the dimensions A, B and U being related by the following formula:

gg=cos U where dA and dB are respectively the increases in A and B resulting from a small increase in temperature of said central portion.

4. An electrical discharge tube comprising a vacuum-tight container having an anode, at least one control electrode and two cathode-support members supported from said container the distance between said cathode-support members and said control electrode being substantially fixed, a tantalum cathode supported on. said cathode-support members and comprising a first portion and two second portions making an angle U therewith, means attaching said second portions to said cathode-support members so that the distance between the ends of said first por-- tion and the end of said cathode-support members is B, the length of said first portion being 2A, and the dimensions A, B and U being related by the following formula:

where CIA and 6113 are respectively the increases in A and B resulting from a small increase in temperature of said central portion.

5. An electrical discharge tube comprising a vacuum-tight container having an anode, at least one control electrode and two cathode-support members supported from said container the distance between said cathode-support members and said control electrode being substantially fixed, a cathode of sheet metal supported on said cathode-support members and comprising a first portion and two second portions making an angle therewith, the dimensions of said cathode being so proportioned to said angle that the changes in said distance which result from a temperature variation of said first portion compensate the changes in said distance which result .from the concomitant temperature variation in said second portions.

RALPH O. McINTOSI-I. GLEN N E. SHEPPARD.

REFERENCES CITED UNITED STATES PATENTS Name Date Le Van Oct. 26, 1948 Number 

